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Unformatted text preview: to build the appropriate ÀÊ ´ µ to eliminate ISI. However, notice that what we want eventually are the samples
at intervals Ì at the receiver. Therefore, we may choose to build a simpler (practical) ﬁlter ÀÊ ´ µ,
take samples at intervals Ì , and put a digital ﬁlter, called equalizer, at the output to eliminate ISI
analog ﬁlter as shown below in Figure 4.9. This approach to remove ISI is usually known as equalization. The
main advantage of this approach is that a digital ﬁlter is easy to build and is easy to alter for different
equalization schemes, as well as to ﬁt different channel conditions.
3 If the matched ﬁlter demodulation technique is employed, the receiving ﬁlter conjugate of ÀÌ ´ µÀ ´ µ.
Of course, we should choose one that can be easily built. 4.9 ÀÊ ´ µ is chosen to be the complex Wong & Lok: Theory of Digital Communications HT ( f ) Ik 4. ISI & Equalization HC ( f ) Impulses Equalizer Decision Equalizer HR ( f ) Decision every T AWGN Figure 4.9: Communication system with equalizer
HT ( f ) Ik HC ( f ) HR ( f ) Impulses every T colored Ga...
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- Spring '08